Experimental Study on Erosion Resistance of Geocells Under Artificial Rainfall

Abstract: It is of great significance to carry out quantitative research on the anti-erosion performance of red soil slope in the low hilly area south of the Yangtze River. Through the slope model experiment, the rainfall scouring tests of different slopes, different rainfall intensities and different cell types were carried out on the revetment of the red loam soil under artificial rainfall conditions. The anti-erosion performance of different cells was quantitatively analyzed. The results show that under the experimental conditions of rainfall, the geogrid has good erosion resistance and obvious effect on rainfall erosion protection of red loam slope, which can be popularized and applied in engineering practice.

Keywords: gravel geocell factory price; artificial rainfall; erosion resistance; red loam

1. Research background

Geotechnical cells first appeared in the 1980s. As a new type of geosynthetics, they have been widely used in geotechnical engineering for their excellent performance. The high quality gravel geocell can be folded and transported easily. After unfolding, it has a spatial three-dimensional structure, similar to a honeycomb shape. The sash can be filled with silt and gravel on the spot. The gravel geocell for sale is resistant to acid and alkali, corrosion, and good integrity, especially the gravel geocell for sale with perforated concrete. It has good drainage in the soil and is beneficial to improve the friction performance between the chamber and the soil. Plants that grow in the soil of the cell can pass through the small holes in the cell and act as a composite reinforcement.

At present, the research on gravel geocell for sale is mainly focused on the horizontal laying of reinforcement foundations in gravel geocell factory price. For example, Jin Shunhao has conducted in-depth research on the mechanism of geogrid-reinforced foundations; Yang Xiaohua et al. on geotechnical chambers on loess embankments and The application of highway slope protection has been studied. The research results of show that the geogrid has an obvious effect on the erosion protection of loess slope, which can generally improve the erosion resistance by 40%, and with the passage of time, the effect It will become more and more obvious that the smaller the size of a single cell, the better the impact resistance; Han Yan, Li Jin, etc. have calculated and applied the stability of the gravel geocell for sale in the slope protection; Wang Guangyue’s geogrid under rainfall conditions The stability of the room flexible slope protection was also calculated and analyzed. However, there are few studies on the anti-erosion performance of high quality gravel geocell slope protection under rainfall conditions.

In China, red soil is mainly distributed in the low hilly areas south of the Yangtze River, including most of Jiangxi and Hunan provinces, southeast of Fujian and Hubei, Guangdong, northern Fujian and Guizhou, Sichuan, Zhejiang, Anhui, Jiangsu, etc. In some parts of the land, as well as in southern Tibet, the study on the ecological protection of red soil slopes is of great significance. In this paper, the anti-erosion performance of the red soil geogrid slope protection under rainfall conditions is tested and quantitatively studied.

2. Test materials and methods

2.1 Test materials
The effective rainfall height of the equipment in the rainfall hall can reach 28m. The earth tank used is a variable slope steel tank. The slope ratio can be changed between 1:15 and 1:2.5. The size of the soil tank is 3m×1.5m×0.5m. Length × width × depth), a partition in the middle of the soil trough divides the soil trough into two parts of size 3m × 0.75m × 0.5m for simultaneous testing. The test soil used the most common Quaternary red loam soil in Dean County. There are 3 geotechnical chambers in the experimental study. The specifications are shown in Table 1. Other test equipments include frog type tamping machine, several U-shaped nails, 3 rain gauges, 36 beakers, 12 buckets (20L), stopwatch, 1 electronic scale with accuracy in grams per cent, and 1 set. Ordinary electronic scales (ranging from 0 to 80 kg), etc.

Table 1 Geocell Specifications

Note: The cell size is indicated by A-B-C, A is the cell height, cm; B is the cell weld distance, cm; C is the plate thickness, mm.

2.2 Test methods
In the test preparation stage, the initial moisture content of the backfill soil was first determined, and it was laminated into a steel tank according to the soil bulk density of 1.25 g/cm3, and compacted by a frog type compactor, each pressing 10 cm thick. Then, geotechnical chambers of different specifications are placed, and U-shaped nails are fixed on the sloped surface, the filling quality is calculated according to the water content of the soil, and then filled into the compartment gravel geocell factory price, and finally, the soil is compacted to the design height and Leveling. For the bare soil slope test, the control group was directly filled to the design height.

In order to ensure that the initial state of the soil in each rainfall test is consistent after each rainfall test is completed, the 20 cm soil layer on the surface of the slope is replaced, and the next test is continued. Before each artificial rainfall, water is firstly poured onto the slope to make the soil basically saturated, which can ensure the same soil water content and ensure the slope flow as soon as possible after the start of the rainfall test. Each geotechnical chamber anti-erosion rainfall test lasts for 30 minutes, every 5 minutes for a period of time. Each time period, a bucket is used to collect water samples high quality gravel geocell. A total of 6 water samples are collected. Each group of water samples is fully stirred and 3 parts are taken from it. A water sample of about 100 mL was placed in a small beaker that had been numbered and recorded with the empty cup mass (m2). After the water sample was extracted, the beaker containing the water sample was weighed again and recorded (m3). Then, all the beakers containing the water sample were placed in an oven at 104 ° C for baking for more than 8 hours, and the dried beaker was weighed again and recorded (m4), and the beaker water sample was obtained by the formula (1). The sedimentation rate W, taking the average sedimentation rate of the three water samples of the same group, can obtain the average sediment concentration S of the corresponding water sample, and then the formula (2) can be used to extract the sediment contained in the water sample of the group. Quality M.

In the formula, m2 is the mass of the empty beaker, g; m3 is the mass of the beaker containing the water sample, g; m4 is the mass after the beaker is dried, and g; W is the sediment concentration of the water sample in the beaker.

M=(m1-m0)×S

In the formula, m0 is the mass of the empty barrel, g; m1 is the mass of the bucket containing the water sample, g; M is the dry mass of the water sample in the bucket, g; S is the sediment concentration of the water sample in the bucket.

The dry mass M of the water sample in the bucket obtained through the above steps is the amount of sediment flushing during the period in the test. The amount of sediment flushing in each group of experiments was cumulatively added in turn, which is the cumulative amount of sediment flushing.

A total of 8 rainfall tests were carried out. During the rainfall test, water samples were collected from the left and right parts of the soil trough gravel geocell factory price. A total of 96 barrels of water samples were taken. Three samples of each bucket of water were taken as one group. After drying, weighing and scouring, Finally, 96 sets of flushing data were obtained. The slopes selected for this test were common 21.8°, 26.6°, 33.7°, and the test rainfall intensity was 50,100 mm/h and 150 mm/h. The schedule of each rainfall test is shown in Table 2.

Table 2 test design

3. Analysis of the anti-erosion performance of geocell

In order to study the erosion resistance of gravel geocell factory price under rainfall conditions, the effects of slope ratio, cell type and rainfall intensity on erosion resistance under artificial rainfall conditions were analyzed.

3.1 Influence of slope ratio change on erosion resistance of geocell
The comparison between the bare slope and the slope of the pavement 2 is shown in Table 3. The cumulative amount of flushing at different slope ratios under 50 mm/h rain intensity is shown in Table 3.

Table 3 cumulative slope amount of slope on different slope ratios

It can be seen from Fig. 1 that after 30 min of rainfall, the slope of the bare soil slope is the largest when the slope ratio is 1:2.0, followed by the flushing amount of 1:1.5, and the total flushing amount of the bare soil is the smallest when the slope ratio is 1:2.5; 20 min The amount of flushing of the back slope ratio of 1:1.5 exceeds the flushing amount of 1:2.5.

Fig.1 The amount of flushing of the non-compartment slope under different slope ratios

Figure 2 shows the amount of flushing of the second slope of the compartment under different slope ratios. As can be seen from Figure 2:
(1) After 30 minutes of rainfall, the relationship between the total flushing amount of the two slopes of the three slopes is basically the same as that of the bare soil slope.
(2) Before 10 minutes of rainfall, the cumulative flushing amount of slope ratio 1:2.0 is small, the cumulative flushing amount of slope ratio 1:2.5 is larger, and the cumulative flushing amount of slope ratio 1:1.5 is between the two.

Fig.2 The amount of erosion of the second slope of the chamber under different slope ratios

The above reasons are analyzed:
(1) After 30 minutes of rainfall, the total flushing amount of bare soil and compartment two slopes is the largest when the slope ratio is 1:2.0, and the slope ratio is the smallest when 1:2.5, mainly because the slope body increases with the slope ratio high quality gravel geocell. The angle of the slope is also increased, but the surface area of ​​the slope is quantitatively constant, so the horizontal projection area of ​​the slope is gradually decreasing; in the case of the same rain intensity, the rainfall received by the slope in the same time is also As the slope ratio increases, the water flow on the slope and the sediment are affected by gravity, and the water flow acceleration will also increase gravel geocell factory price, and the unit flow water flow handling capacity will be enhanced.
(2) When the slope ratio increases from 1:2.5 to 1:2.0, the flow rate of the water flow on the slope will increase, which will increase the total flushing amount; when the slope ratio increases from 1:2.0 to 1:1.5 The rain area on the slope is reduced, and the water flow on the slope has a major effect, so the total flushing amount of the slope is reduced.

In short, the slopes of the two slopes with different slopes under the same rain intensity have more significant impact effects.

3.2 Influence of different types of geocells on erosion resistance
The corrosion resistance of different types of gravel geocell for sale under different rain intensities was observed and analyzed.

It can be seen from Fig. 3 that after 30 minutes, the soil erosion resistance of the lattice slope under three kinds of rain intensity is more obvious than that of the bare soil slope. In Fig. 3(c), before 15 minutes, the cumulative flushing amount of the bare soil slope is larger than the cumulative flushing amount of the paved slope. The reason for the analysis is that the slope surface of the compartment is relatively loose. When the rain intensity is large high quality gravel geocell, the water flow is relatively large, and the soil is more susceptible to water flow, so this period The amount of sediment flushing is larger than that of bare slopes. As the scouring time is prolonged, the function of the cell is better reflected, which not only hinders the water flow, but also the surface soil is protected by the space in the space and is not easy to form a long and long gully, but the bare slope will cause The scouring continues to produce some fine grooves or even gullies, which exacerbate the erosion of the soil. Therefore, the long-term flushing will cause the total erosion of the bare slope to exceed the slope of the paved compartment.

Fig.3 Variation of flushing amount of slopes with different rain intensity and different cell types

After 30 minutes of rainfall, under the rain intensity of 50mm/h or 100mm/h, the test results are consistent with the erosion test of the loess slope by the gravel geocell factory price made by. The general trend is that the smaller the grid sash, its erosion resistance. The better. However, the anti-scourability of compartment 1 is relatively poor. The total amount of flushing between compartment 2 and compartment 3 is not much different. The reason is that the smaller the grid, the better the erosion resistance of the solid soil. The smaller the grid is, the more difficult it is to fill the sash and the more difficult it is to construct. The compartment 3 is too small, and the soil in the sash is looser than other compartments. When the rain intensity is small, that is, 10mm/h, the slope is mainly affected by the splash of raindrops, and the soil on the slope of the three slopes is relatively loose, so the erosion of the slope is large (see Table 4 for details).

Table 4: Geogrid sash size is different under different conditions

Slope flushing (slope ratio 1:2.0) g

3.3 Influence of artificial rainfall intensity on erosion resistance

The effects of different artificial rainfall intensity on the impact performance were analyzed by the amount of sediment flushing of different rain strength downhills.

The analysis shows that as the rain intensity increases, the total flushing amount of the slope increases, but it does not have a linear relationship. When the rain intensity increases from 10mm/h to 50mm/h, the rain intensity increases by 5 times, and the number of flushing increases by nearly 5 times; but the rain intensity increases from 50mm/h to 100mm/h, and the rain increases. When the size is 2 times larger high quality gravel geocell, the amount of flushing is increased by nearly 20 times. The reason may be that the flow rate of the slope surface generated by the small rain intensity after the surface flow is small and the flow rate is small, and only the small sediment particles can be transported, and the larger rain intensity has a stronger carrying capacity, and the slope is stronger. The damage caused by the surface is also greater, and it is prone to gully erosion, which in turn will increase the amount of sediment erosion. The slope of the compartment is paved. When the compartment buried in the soil partially exposes the soil, the part of the compartment beyond the surface of the slope has a certain energy dissipation and hindrance effect on the slope flow, which reduces the handling capacity of the water flow. And the surface soil is protected by the compartment in space and is not easy to form a large and long gully erosion, so the slope surface with the compartment has better corrosion resistance.

4. Conclusion

(1) The geotechnical chamber has a certain protective effect on the rainfall scouring of the red soil slope. With the continuation of rainfall, the slope protection effect of the compartment will become more and more obvious. This is related to the observation of the slope protection experiment of the geotechnical compartment of the loess slope by Wang Guangyue et al. Basically the same, there is a certain mutual reference between the red loam soil and geogrid slope protection and the loess geogrid slope protection.
(2) The smaller the grid frame is, the better the rainfall resistance of the red soil slope is, but the smaller the grid is, the more difficult the construction fill is, which is easy to affect the protective effect of the compartment. Therefore, the type of compartment should be based on a specific project. Need to make a choice.
(3) Under the condition that the rain intensity is 50mm/h and the slope length is constant, the slope is 21.8°～33.7°. With the increase of the slope, the erosion resistance of the gravel geocell for sale slope is first reduced and then increased, and the slope is 21.8°. At the time, the erosion resistance of the high quality gravel geocell slope is the best.

In summary, the gravel geocell for sale has an obvious protective effect on the rainfall erosion of the red soil slope, which can be promoted and applied in engineering practice.